A Computed Tomography (CT) device (a short for computer tomography scanning system) is a common instrument for medical imaging diagnosis. Simply speaking, the CT device is to perform tomography scanning with X rays.
A structure and principle for a CT device is as follows. A tube is used as a ray source, an electron beam, generated from a cathode of the tube under an effect of a high voltage filament, shoots at an anode target to be refracted as rays in a fan geometry, and then scanning and imaging are performed by using the rays to implement imaging diagnosis, as shown in FIG. 1.
Due to a high requirement on accuracy of a medical CT device, control for rays in the CT device is extremely rigorous. Focus position of the rays is critical for controlling the direction and angle of the rays. The so-called focus refers to a point where the electron beam is refracted on the anode target. The focus may be considered as a source of the rays, and the accuracy of the focus position is the basis for achieving accurate control of the rays. Once the focus position has an error, the direction and the angle of the rays may be significantly affected.
Unfortunately, the generation and control of rays in the tube of the conventional CT device generally depend on mechanical components to some extent, and therefore the derived mechanical error is unavoidable. In practical application, when the angle of the rays is changed, a rotation of the anode target, a rotation of a gantry, cold shrinkage and thermal expansion of the anode target may affect the focus position. As shown by the dashed lines in FIG. 1, as the anode target and the gantry rotate, the anode target shifts to the position represented by the dashed line due to an effect of gravity; and the focus and the rays are also shifted due to the shift of the anode target. Referring to the X-Y-Z spatial coordinate system shown in FIG. 1, the rays shift in X-axis and Z-axis respectively.
In conventional technology, correction of shift in focus position is normally confined in a mechanical level. For example, by providing a ray detector to detect the change in radiation position of the rays on the detector and by adjusting related mechanical components accordingly, a constant radiation position on the detector is ensured and a correction for the position is achieved. However, such a conventional mechanical method, naturally subjected to a restriction of mechanical movement, is hard to realize quick correction in real time and has a relative slow adjustment speed; and hardware modification in connection with the mechanical method brings relatively high cost.